Balanced thermostat



y 935. H. J. SMITH BALANCED THERMOSTAT Filed Feb. 23, 1933 TOR ATTORNEY Patented July 9, 1935 UNITED STATES PATENT OFFICE Application February 23, 1933, Serial No. 658,051

12 Claims.

This invention relates to condition-responsive devices and more particularly to a pressure-responsive device of the expansible bellows type.

An object of the invention is to provide a pressure-responsive device having high sensitivity.

Another object is to provide a device of the above-mentioned type which may be readily adapted for a variety of pressure ranges.

Another object is to provide a cheap, simple, efficient and dependable device of the type above indicated.

Although the novel features which are believed to be characteristic of this invention will be more particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages and the manner in which it may be carried out, may be better understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof, in the various figures of which like reference characters have been used to designate like parts.

In the drawing:

Figure 1 is a side elevation, partly in section, of a thermostat illustrating one embodiment of the invention;

Figure 2 is a section taken on the line 2-2 of Figure 1; and

Figure 3 is a detail of the switch arm and 00- operating contacts.

Referring to the drawing, the invention is shown as embodied in a pressure-responsive device comprising a housing l0, which is mounted on a bracket H by suitable means, such as a clamp l2, which is adapted to surround said housing and to be secured to said bracket in any desired manner (not shown). The housing 10 is sealed by a cap 13, which may be seated in a. flange l4 formed on said housing.

An ekpansible bellows l5 having a comparatively stiff cover l6, hermetically sealed thereto to form a variable pressure chamber, is mounted within the housing I0. A plunger l! is rigidly secured to the cover l6 and extends through a bushing l8 carried by the cap J3. A second metallic bellows I9 is seated in a recess 20 in the cover l6 and is secured between the cap l3 and the plunger H to form a glandless seal for the plunger. The bellows I9 also serves in conjunction with the cap l3 and the bellows l5 to form a hermetically sealed balancing chamber 21 within the housing I0 and external to the bellows To operate as a thermostat, for example, the bellows l5 may be charged with a substance hay-=- ing a substantial change in vapor pressure within the temperature range involved in the operation of the device. The amount of charge is preferably such that the vapor remains saturated, in the presence of its liquid, only throughout the operating range, inasmuch as the differential change in vapor pressure of the saturated vapor with respect to temperature is greater than the differential change in gas pressure of the unsaturated vapor.

Various substances may be employed for this purpose, depending upon the operating range of the instrument. Methyl chloride has been found suitable for an outdoor thermostat having a temperature range of, for example, from -l0 F. to F. Various other substances which may be employed, together with representative temperature ranges, are as follows Isobutane 10 F.- F. Butane 33 F.- F. Ethyl chloride 60 F.-l40 F. Sulphuric ether F.-180 F. Carbon tetrachloride F.-220 F. Alcohol 180 F.260 F.

All of the above representative substances have a substantial vapor pressure within the range of temperatures specified and possess a comparative 1y high differential pressure with respect to temperature, provided the amount of the charge is such that the vapor always remains saturated. It is obvious that other substances having similar properties may be employed.

The chamber it may contain any counter-balancing gas, such as air. The relationship between the size, gas pressure and change of volume of the balancing chamber 2i is preferably such that the pressure-volume curve of the gas within the chamber follows the pressure-temperature curve of the substance within the bellows l5.

Adjustment for this purpose may be made by introducing into the chamber 2i a liquid, such as alcohol, so as to reduce the gas volume of the chamber without reducing the total volume change of the chamber. By this means the ratio of the maximum to minimum gas volumes in the operating range of the device may be raised to any desired value. The. liquid reduces the movement of the bellows per degree of temperature change and consequently increases the tem perature range of the device. It also permits the use of a bellows that is comparatively long with respect to the total change in length during operation.

For example, if the liquid occupies 0.9 of the volume of the bellows in its expanded position, it is evident that a movement of only 0.1 of the total length of the bellows changes the gas volume from a maximum to and changes the gas pressure from a minimum to infinity.

As a further illustration, the change in vapor pressure of methyl chloride between 0 F. and 65 F. is equal to approximately 58 pounds per square inch. Hence, if the bellows I is charged with methyl chloride, the volume ratio of the balancing chamber 2! should be such that a pressure difierential of 58 pounds is obtained in the same range.

The adjustment is preferably made at the lowest working temperature so as to avoid the necessity for allowing for shrinkage of the gas upon reduction in temperature. For convenience, the adjustment may be such that the counterbalancing gas is at atmospheric pressure at the lowest working temperature. The liquid may be introduced from any suitable source (not shown) through an inlet pipe 25, provided with a valve 26. When a suflicient amount has been introduced to produce the desired operating characteristics, the pipe 25 may be removed and the opening in the cap I3 may be sealed by suitable means, such as by solder.

The arrangement is such that the vapor pressure within the bellows i5 is nearly equal to the gas pressure within the chamber M. It is possible, therefore, to utilize a bellows having extreme sensitivity because of the relatively small pressure differential to which it is subjected. The bellows 85 may accordingly be formed with a comparatively thin wall and may be made much more flexible and sensitive than would be the case if it were exposed externally to the atmosphere. The bellows i9 is of small diameter and of comparatively great length and may accordingly be made to withstand the difference between the pressure in the chamber 25 and the pressure of the outside atmosphere without being unduly rigid.

With a rise in temperature, the pressure of the substance within the bellows it increases and the bellows expands to equalize this pressure against the pressure in the chamber 2i, thereby producing longitudinal motion of the plunger ll. Upon a fall in temperature, the reverse action takes place.

The plunger l'il may be connected to any suitable mechanism in which mechanical movement is desired in response to temperature or pressure changes, such, for example, as a heat control (not shown). It is illustrated, for example, as applied to the control of a reversing and progressive switch mechanism comprising a lever 3b which is connected to the plunger ll by suitable means, as by a pin 3i engaging a slot 32 in said lever. The lever 3i! is pivoted about an eccentric stud 33 on a pin 36, which is supported on a base plate 35 in any convenient manner, as by screws 65, engaging flanges 416 formed on or secured to the pin ti l. The base plate 35 carries a plurality of sets of contacts 36 and 371 and may be secured to the bracket H by suitable means, such as screws 38.

The lever 30 carries a pair of contact members 36 and M, which are adapted to cooperate with contact members 62 and it respectively, carried by a switch arm 341, which is pivoted about the pin 3%. The switch arm l carries brushes 5i and 52, which are electrically connected to the contacts t2 and 63 respectively and are adapted to selectively engage the sets oi contacts 36 and 31 respectively. The contacts 40 and ti may be connected by flexible connectors 55 and 56 to binding posts 57 and 58 respectively. The binding posts together with the sets of contacts 36 and 37 may be connected to a multiple socket 6d, which facilitates connection of the device to an operating unit (not shown). I

The eccentric mounting'of the lever 36 causes the contacts it and ii to slide over the contacts t2 and 33, respectively, when the switch arm 44 and the lever 30 are oscillated, thereby tending to maintain the contacts in clean condition.

The above-described switch mechanism is adapted to constitute a reversing and progressive switch, which is operated by the thermostat and may be used to control a reversible conditioncontrol device of any desired type, for example, a reversible motor control unit disclosed'in my copending application Serial No. 657,237, filed February 17, 1933.

The above-described device has been found to be particularly sensitive and powerful and may be adjusted to produce any desired movement of the plunger i? for a given change in temperature. It is accordingly particularly adapted to heat-control systems and the like, wherein a fine control of temperature is required. It is also adapted for various other uses, which will be apparent to a person skilled in the art.

The invention has been specifically described for convenience as embodied in a thermostat, but it is obvious that it is applicable to any variable pressure device. The bellows i5 may, for example, be charged with steam from a steam line and may operate in response to pressure variations thereof.

Although a certain embodiment of the invention has been disclosed for purposes of illustration, it is to be understood that the various parts thereof may be varied without departing from the spirit of the invention, and that the inven-- tion is only to be limited in accordance with the following claims when interpreted in view of the prior art.

I claim:

l. A thermostat comprising an expansible bellows, a housing surrounding said bellows and forming a hermetically sealed balancing chamher, a plunger operatively associated with said bellows and extending through said housing for longitudinal movement with respect thereto and being hermetically sealed to said housing.

2. A thermostat comprising an expansible bel-,

lows, a housing surrounding said bellows and forming a balancing chamber external thereto, a plunger operatively associated with said bellows and extending through said housing, and a second expansible bellows associated with said plunger and forming a glandless seal with said housing.

3. A thermostat comprising an expansible bellows, a housing surrounding said bellows and forming a balancing chamber external thereto, a plunger operatively associated with said bellows and extending through said housing, and a second expansible bellows associated with said plunger and forming a glandless seal with said housing, said first bellows being adapted to withstand a small pressure difierential and said second bellows being adapted to withstand a greater pressure difierential.

4. A thermostat comprising an expansible bellows having a cover hermetically sealed thereto, said cover having a recess formed therein, a housing surrounding said bellows and forming a hermetically sealed balancing chamber external to said bellows, a plunger secured to said cover and seated in said recess and extending through said housing, and a second bellows interconnecting said plunger with said housing and hermetically sealing the same, said second bellows being of less diameter than said first bellows and being of comparatively great length and adapted to withstand a greater pressure difierential than said first bellows.

5. In combination, a temperature-responsive device comprising an expansible bellows, a housing forming a balancing chamber external to said bellows, a. plunger operatively associated with said bellows and extending through said housing, a switch means comprising a stationary plate carrying a set of progressive contacts, a brush pivoted to progressively engage said contacts, and means associated with said plunger for controlling the position of said brush.

6. A switch mechanism comprising a contact, a pivoted lever carrying said contact, a second contact, a switch arm pivoted eccentrically of said lever and carrying said second contact, and means for causing pivotal movement of one of said contacts, said eccentric mounting being adapted to cause relative sliding movement between said contacts for maintaining said contacts in clean condition.

"7. A switch mechanism comprising a pivoted switch arm carrying a pair of contacts and a lever pivoted eccentrically of said arm and carry- .ing a second pair of contacts adapted to cooperate with said first pair of contacts to form a reversing switch, the eccentric mounting causing relative sliding movement between said first and second pairs of contacts when said arm and lever are oscillated, whereby said contacts are maintained in clean condition.

8. A pressure-responsive device comprising an expansible bellows, a rigid housing surrounding said bellows to form a balancing chamber, the pressure in which is varied by movement of said bellows, said chamber being partly filled with a liquid adapted to decrease the gas volume thereof and to increase the volume ratio of the chamber within the operating range thereof while permitting the use of a long, flexible bellows.

9. A pressure-responsive device comprising expansible means forming a variable pressure chamber, said chamber being partly filled with a liquid adapted to displace a part of the gas content and to reduce the total gas volume of the chamber while permitting the use of a long, flexible bellows, whereby the differential gas pressure with respect to the total volume of said chamber is increased.

10. A variable pressure device comprising a bellows containing a variable pressure medium, a housing surrounding said bellows and sealed to form a balancing chamber, said chamber containing a liquid and a gas, said liquid being adapted to decrease the gas content of said chamber, whereby the volume ratio of the gas within the operating range is increased with respectto the total volume ratio of said chamber, said liquid being in such quantity as to cause the volume-curve of the gas to correspond to the pressure-curve of said variable pressure medium within a selected operating range.

11. A housing having expansible means adapted to form a variable volume chamber, said chamber containing a gas and a liquid, said liquid being adapted to displace a part of the gas and to reduce the gas volume by a constant amount throughout the operating range of the device, whereby the pressure-change of the gas with respect to the total volume-change of said chamber is increased.

12. A housing having expansible means adapted to form a variable volume chamber, said chamber containing air and alcohol, said alcohol being adapted to displace a part of the air and to reduce the air volume by a constant amount throughout the operating range of the device, whereby the pressure-change of the air with respect to the total volume-change of said chamber is increased.

HAZOR J. SMITH. 

